Rotor for induction motors



May 11 1926.

7M' J a TTORNE yf,

H. 1 TANNER ROTOR FOR INDUOyION MOTORS Filed June 14, 1921 `willhereinafter appear,

effect 'in the tube,

5o l vantage when this ,Patented vMay '11, 1926.

, UNI-Tao s'TrEs PATENT DF-Cm y y:Misafir L. annua, or Baooxmm.NEwlronx, salomon 'ro son nisrnuu'mrr co ANY, me., or Ymaw You, N. Y., Aconromyrron or Naw Yoan.

" Boron ron rNnUcfrIoN amorous.

Fappucation med .rime 14,

squirrel cage type -for use 1n small "induction motors ada ted to besupplied with current of relatively high frequency and which require' tobe started under load. Under these conditions such motors will notrapidly attain their normal speed onac count of the high reactance ofthe rotor conductors when the motor is started and the consequent llowtorque due to.the lphase fdiierence between the iux produced bythestator and the current in the rotor.

It is an object of the invention toprovide a rotor of the squirgel cagetype par` ticularly adapted for use in ,motors of the labove characterand which will have a large torque at starting, but which when it hasattained Efull speed will run with low slip under operating conditions.i

A. further object of the invention is the provision of a rotor havingthe above characteristics which shall be ofv simple construction, strongand rigid and be otherwise adapted for use in -sma high speed inductionmotors such, for instance, as gyrosco es and the like designed to besupplied wit polyphase current of relativelyA high frequency. l

The above objects, as well as others which are attained by the'provision of a squlrrel cage rotor in which each 'of the low resistancebars is surrounded by a tube of high resistance, magnetic materialforming with the bar, aparallel path in which the current will be morenearly in hase with the flux of the rotating mag- Y netlc eld than isthe current in t e bar thus giving the torque required for starting Thepresence of the low resistance bar withiin the high resistance tubeincreases the skin thus increasing the eifec- .tive 'resistance ofthelatter to the current "whichlows throughit,..--f --'flhe' constructionp'ermi ductin" 'bars ofv circularfcross sectionI which have t e maximumAreactance v'for a' given current carrying capacity.A and make the bestuse of the space within,y the magnetic materialfofA the rotor,-whiclrisof especial-adfsp'ace-s' limited as itis By forming fthe tubes of Linll1 motors? -v y A mounted'-abearin ts the use of con- 'extends-into a'.bearingl v'l-iel .provided wih a 'which lubricantmay ow "f5 fx-omi'whicli'l-:it -11s umped 'to the mage-eue una@rial'- aihighlresismneepath in f1' The bear' 1921. serial m. 477,441.

tity of magnetic material in the rotor.

If the tubescompletely surround the conductor's, the rotor',l will havea high starting torque, but there will be an excessive shp at normalspeed. In order to overcome this dlsadvantage each tubeis slottedlongitudinally on the side toward the stator. The wider the slots themore nearly will the rotor run at synchronous speed', but the less willbe the effect of the tubes in reducing-the current in the conductorswhen the rotor is' starting. By suitably proportioning' the eol width ofthe slots'a, compromise maybe ob.

tained which will give the best result be- -tween the two conflicting reuirements.

The particular nature of t e invention as well as other objects andadvantages thereof will appear more clearly from a description of apreferred embodiment. For `purpose oil illustration the rotor structureof the inventionwill be described inconnection with an induction motorconstituting a gyroscope as shownin the accompanying drawings in wh1chFig. 1 is a plan view partly in section of the gyroscope,

Fig. 2 is a sectional'elevation taken along the lme 22 of Fig. 1,

Fig. 3 is a detail view of a tube of a conductor,

Fig. 4 is a similar view vof an inner bar of a conductor and Fi'g. 5 isan enlarged construction of one of surrounding tube. p

The gyroscope comprises a'c'ase 1 anda cover 2 clamped togethervby.screws 3, thel view showing the end case bein provided withdiametrically op posite'soc ets 4 adapted-to vreceive the bearmgs bywhich the roscope may' 'besupported. The casey). lsfprovided atits-bot-v the rotor-bars and its am waha housmg .-15 Within-v whieh-ais6V fffcr -the lower endv of the upper end of vwhich 8 within'a'housing ecover 2.' The case passage 9 thleugh from the up ler* into the cham 0rPP?? bearingS-fthrou'gh a.- j re in the shaft-7.-t

a 'taperingshaft' formed at the-top of t portions of the apparatusstaff-alie shaft andere ,j

pum ed through the shaft to the upper beari gl orm the subject matter ofmy co-pending application Serial No. 477,432 filed June 14, 1921, andtherefore will not be described in detail herein since theyconstitute nopart of the resent invention.

The .bottom of the case 1 is provided with a circular recess 10 adaptedto receive a flange 11 at the bottom of a tubular member 12 whichsurrounds. the shaft 7 and serves as a support for the stator 1,3 whichis made up in the usual manner-ofa laminated core 14 and windings 15,vthe terminals 16 of which are carried through an insulating bushing 17set within the flange 11 and the bottom of the case 1. lThe case of thestator is supported upon a' shoulderon the outside of the member 12, andprevented from turning by a key 18. Since the stator may be of anydesired construction adaptedto cooperate with the squirrel-cage rotor ofthe invention, it will not be described in further detail.

Mounted upon the upper portion of the shaft 7 is the rotor or wheel 19of the ro-4 sco e. The hub 20 of this rotor is prov1ded wit a borehaving a taper corresponding to that of the shaft 7 so that it may beheld firmly thereon by means of a nut 21 screwed upon a threaded portion22 of the shaft. The outer annular portion 23 of the rotor 1s relativelythick in order to give the requlred mass to the rotating member of theroscope. Thisportion of the rotor is provided with a cylindrical innervface within which are mounted the parts constituting/its elec? tricaland magnetic elements. Thesevparts .consist'of a series of ironlaminations 24 clamped between conducting end rings 25 by means of bolts26. The end rings and the laminations are provided at their mner edgeswith a plurality of apertures within-which are placed the conductors ofthe' rotor. VEach of these conductors consists of a cylindrical memberor bar 27 of conducting material, such as copper, surrounded by a memberor tube 28 of magnetic material having a com-' paratively'highresistance, such as iron.

As shown most clearly in Fig. 5, which shows the upper end of one of theconductors- 'of the rotor, the bar 27 is bevelled or cham-l fered as at29 while the outer edge of the tube 28 is likewise bevelled as at 30.`When these members are inserted within the cylin- -rical aperturesprovidedthrough the end plates and laminations of the rotor there arethus formed two 1channels within' which suitable soldering or brazin.material 31 may be poured to insure good etween the members and the endring 25 as well as to `aid in holding `these members firmly in place. Ansolderin material that mayproject abovejt e upper ace ofthe end plate 25may be removed in any suitable mauneriso as toleave the outer surface ofthe rotor, lies increase the lirmness ve eetrical connections,

tllle mhterial flush with the face of the end ate. P. As shown mostclearly in Fig. 3, each of the tubes 28 is provided with slot l32 which,when the tube is in place in toward the inner face of the` rotor, ortoward the stator as shown most .Clearly in Fig. 1. When filling thechannels with the soldering material somel of it may run into the upperend of the slot in the tubular member as-shown at the right of Fig. 5,but this will do no harm and will with which the bar 27 and itssurrounding member 28 are held in place.

1t is intended that the tratedf'in the drawings and shall be operated bythree relatively high frequency, but it will be vunderstood thatthenumber of phases and the frequency is immaterial so` far as theapplication of the invention to any other type of induction motor isconcerned. It will also be understood that the stator may bel. providedwith any desired number, of po es.. Y

As the alternating current begins to flow through the statorwindings toproduce a rotating field there set up in the con-- gyroscopeillusdescribed above will be ductors of the rotor currents which will bea longitudinal phase current of of substantially the same frequency asthe'.

The reactance of the bars 27 to the current of hi'h line current.

cause a large difference in phase between the frequency which Howslthrough them as the motor is started'will ofthe rotor due to thecurrent linfthe bars will be low, and due to its mass a considers abletime will be required for it to come up 'to normal speed. This would beparticularly objectionable in the case ofa gyroscope used as part of agyroscopic compass or any other form of nautical apparatus.

Due to the relatively high resistance of the surroundin tubes 28 thecurrent which flows through tiem when the rotor is starting will be morenearly in phase with the flux produced by the stator. This current willproduce the torque required to ra idly bring the rotor up to normalspeed, t ereby making up for the lack of torque of the current in thebars 27. The current inthe bars27 within the tubes 28 will also increasethe skin effect in the tubes thereby still further increasing theeffective resistto speed, and thereby cause an excessive de-` vwill bean advantage under running conditions as it Will reduce the slip of therotor. In practice the slots will be' of a suitable Width to give thebest results under both starting and running conditions, the Width forany particular rotor depending upon the characteristics of the motor inwhich it is to be used and the service for which the -motor is intended.

Not only does .the presence of the surrounding tubes increase thestarting torque of the rotor, but this result is accomplished withoutrequiring that the cross-section of magnetic material in the rotor bereduced since the tubes are formed of magnetic material. The bars of theconductors' may be of circular cross section which gives the.

' maximum reactance for a given current carpath 1n slstance acity andoccupies less of the space within t e iron of the rotor than does anyother form of bar. This is of 4vparticular advantage in the case ofsmall motors.4 The arrangement thus gives a.l high resistance parallelwith each of the low rears without interfering in any Way with the areaof the surrounding iron.

The `rotor construction described above possesses, in addition to itsadvantages from' the standpoint of operation, many mechanivcaladvantages which render it particularly adapted for use in connectionwith motors which should be driven at high speed, such as lgyrosoonesand the like. These advan tages reside inthe simplicity and strength ofconstruction and in the lack of any tendency for the conducting membersto shift Within the laminations ofthe rotor since the tubes serve assupports forthe bars and the i presence of the soldering material at theends of the members increases the security with which they are held inplace.

While the invention has been shown and described in connection with aparticular form of induction motor, i. e., a gyroscope, it willbe'understood thatit is equally applicable to induction motors adaptefor other purposes and also that various changes in the details ofconstruction of the elements of the invention may be made Withoutdeparting from the principle thereof as delined in the appended claims.

I claiml. A dynamo-electric machine rotor comprising conducting endrings, core laminanations between said rings, a plurality of cylindricalconductors extending through said laminations to the outer surfaces ofsald rings, and axially slotted conducting tubes sheathing and retainingsaid conductors, said tubes having circumferentially chamfered endsconnected to said rings with fusible conducting material.

2. A dynamo-electric machine rotor comprising conducting end rings, corelaminations between said rings, a plurality of conductors extendingthrough said laminations to 'the outer surfaces of said rings, .andaxially slotted conducting tubes sheathing and substantially as long assaid conductors, said tubes having their ends connected to said ringsand conductors with fusible conducting material.

In testimony whereof I afix my signature.

v HARRY L. TANNER.

